1. Field of the Invention
The present invention relates generally to heat exchanger devices, and more particularly to a compact heat exchanger with corrugated polymeric tubing for use with high purity and/or corrosive fluids.
2. Description of the Background Art
Many industries require the use of heat exchangers to regulate the temperature of high purity and/or corrosive fluids. For example, microchip fabrication within the semiconductor industry requires heating and temperature regulation of the etching solutions used to etch silicon wafers and microcircuit lines. Because both the process temperatures and the heat capacities of the etching fluids are relatively high, a rather large amount of heat is required to raise and maintain the temperatures of the etchants.
Additionally, etching fluids must be free of foreign particles in order to avoid the contamination and destruction of microcircuits formed in the silicon wafers. Therefore, because etching chemicals, such as hydrofluoric acid, are harsh and corrosive, the etching fluid must not come in contact with any portion of the heat exchanger which could corrode and/or dissolve, thereby introducing contaminants into the etchant.
Attempts have been made to overcome these limitations. For example, thermally conductive oil or grease is often placed between the tube and heat exchanger. Additionally, coiled inserts are sometimes placed within the tube (see e.g., U.S. Pat. No. 5,899,077 to Wright, et al.). While the turbulence caused by the inserts facilitates increased thermal transfer between the heat exchanger and the fluid, the inserts also cause xe2x80x9cdead zonesxe2x80x9d within the fluid flow, increasing the potential for particle build-up and contamination of the etching fluid.
In addition, it is also hard to form tight bends in known tubing materials. This creates several problems when designing and manufacturing heat exchangers, wherein tubing typically includes multiple bends. First, known inert tubing is easily kinked, and cannot therefore be bent into small diameter bends. Rather, such tubing requires a large bend radius, and is therefore often bent outside of the heat exchanger, thereby reducing the heating efficiency of the heat exchanger. Further, as the wall thickness of the tubing decreases, the required bend radius increases. Alternately, if the tubing is entirely retained within the heat exchanger, a complex curved channel with large bend radii must be machined into the heat exchanger plating. In either situation, because of the large bend radii of plastic tubing, less tubing can be used per unit surface area of the heat exchanger, thereby reducing the thermal efficiency of the heat exchanger.
What is needed, therefore, is a heat exchanger that utilizes tubing that can withstand high working temperatures without rupturing or becoming diffusive. What is also needed is a heat exchanger that improves thermal conductivity between the tube and the heat exchanger, while remaining compact, highly expandable, inexpensive to produce, and easy to maintain.
The present invention overcomes the problems associated with the prior art by providing a novel heat-exchanging device. The invention facilitates high temperature heating of high-purity and/or corrosive fluids by utilizing temperature resistant tubing having corrugated bends formed therein. The unit is compact, inexpensive, expandable, and easy to maintain.
The disclosed particular embodiments of the heat exchanger include at least one thermal reservoir and a tube in thermal contact with the thermal reservoir that has corrugated bends. The tube is formed from a chemically inert material (e.g., perfluoroalkoxy (PFA) plastic), and has relatively high working temperatures (e.g., exceeding 250 degrees Celsius). In the disclosed embodiments, the tube has a plurality of straight sections and a plurality corrugated sections.
In a particular embodiment, the thermal reservoir includes at least one plate having a channel formed therein to receive the tube. The channel has straight sections and curved sections, in which to receive the straight and corrugated sections of the tube, respectively. The straight sections of the channel (and thus the tube) are arranged parallel to one another, wherein the spacing between consecutive straight sections is less than or equal to twice the diameter of the tube. The curved sections of the channel within the plate have a wider diameter than the straight sections in order to accommodate the corrugated bends of the tube. In a more particular embodiment, the thermal reservoir includes a second plate, having a complementary channel to the channel formed in the first plate. The second plate is fixed to the first plate. In another particular embodiment, the heat exchanger comprises multiple thermal reservoirs fixed together, and is capable of simultaneously heating multiple fluids and/or additionally heating a single fluid. In a particular embodiment, the fluid conduction tube passing through a first thermal reservoir is connected to the fluid conduction tube passing through a second thermal reservoir.
The thermal reservoir(s) of the various heat exchangers are heated and/or cooled in a variety of ways. In a particular embodiment, at least one heater is secured to the thermal reservoir(s). In a more particular embodiment, the heater is a cartridge heater disposed in or between one or more plates or thermal reservoirs of the heat exchanger. In an alternate embodiment, thermoelectric chips are coupled to the outside of one or more thermal reservoirs. Optionally, a heat sink can be secured to the thermal reservoir to prevent the thermoelectric chips from overheating, as well as, to regulate the temperature within the thermal reservoir.
The fluid conduction tubes of the heat exchange sub-units can be configured in a variety of arrangements. For example, the tubes of adjacent heat exchange sub-units can be connected in series or in parallel. Indeed, the heat exchange sub-units of an expanded heat exchanger can be configured in any combination of in series or in parallel groups.